Deep Water Horizon oil and methane carbon entered the food web in the Gulf of Mexico

The Deep Water Horizon (DWH) incident caused the release of an unprecedented amount of 13C- and 14C-depleted oil and gas to the Gulf of Mexico (GoM), which formed surface slicks and deep oil/gas plumes that extended laterally at 1000–1200 m. We conducted three research cruises between 2010 and 2012 to study the potential assimilation of petrocarbon (C derived from oil and/or gas) into the GoM microbial food web. In 2010, we found low δ13C (−30 to −25‰) and Δ14C (−603 to −55‰) values for suspended particles at 1000–1200 m depth as far as 289 km SW of the wellhead, providing direct evidence of the spatial extent of the subsurface plumes. At those depths in 2010, methane and oil carbon accounted for up to 28% and 62% of total particulate carbon (Csp), respectively. In the total area affected by the DWH, 80 ± 56 to 104 ± 91 tonnes (t) of methane-derived and 216 ± 174 to 292 ± 165 t of oil-derived carbon were incorporated into Csp. In 2011 and 2012, the δ13C values were distributed throughout the water column indicating that petrocarbon was still present and recycling, especially in the section closest to the DWH, where oil supplied up to 53% and 75% of Csp, respectively. Relatively low δ15N (< 4‰) values in suspended particles at 1000–1200 m in 2010 indicate stimulation of nitrogen fixation linked to methane oxidation in the months after the spill, which accounted for up to 40% of the particulate nitrogen in the water column at those depths.